1. Field of the invention
This invention relates to a reciprocating fluid pump and, more particularly, to a low pulsation displacement pump having a discharge stabilizing function which is suitable for use in analyzing devices.
2. Description of the prior art
The low pulsation displacement pump of the type disclosed in U.S. Pat. No. 4,600,365 is structured to conduct suction and discharge in such a manner that a pair of plungers are alternately and complementarily operated by means of cams. In a pump of the type referred to above, the shape of the cam is specifically designed to reduce generation of pulsating flow and thereby to keep constant the composite discharge effected by operation of the two plungers.
However, in the above-described prior art, the accuracy of discharge depends upon the accuracy of the machined parts, such as cams and plungers. This raises a problem that the fluid discharge cannot be stabilized to a degree which exceeds the accuracy of manufactured parts.
To deal with this, a method could be conceived in which past errors are stored in a memory and the fluid discharge is compensated in accordance with this stored data. In this method, the discharge pressure is measured and any variation is used to compensate the rotational speed in a succeeding rotational cycle of the cams. However, in the practical analysis, there is another problem that other factors which influence accuracy are involved, such as entrapment of air bubbles and valve-switching noise. It is, therefore, difficult to conduct ideal error correction. Furthermore, the method of correction which depends upon past data raises a problem that the reproducibility which is necessary for analyzing devices is lowered.
Therefore, a low pulsation pump was disclosed in U.S. Pat. Application Ser. No. 111,640 by Taro NOGAMI et al (and in EP Application No. 87115449.8). This low pulsation pump conducts the correction of fluid discharge only in the period of suction and discharge where a large ripple effect is involved. In this low pulsation pump, however, the accuracy of the fluid discharge in other periods depends upon the accuracy of machined cams. This leads to the fact that any error in the manufacture of cams causes a variation in the fluid discharge of the pump.